In recent years, the number of people who conduct remote conversations by using transmission terminals, such as personal computers (PCs) or mobile phones, is greatly increasing. Furthermore, it is becoming possible to conduct conversations not only between two places (two people) but also among multiple places (three or more people).
An operator who operates a communication service that enables conversations between the transmission terminals makes a profit by charging users of the transmission terminals communication charges. As a method for charging the communication charges, there is a method for uniformly charging all users (participants) who have participated in a conversation the communication charges for a period from start to end of the conversation (see Japanese Patent Application Laid-open No. H9-172509, for example).
However, for example, there is a case that a user using a different transmission terminal joins in a conversation while the conversation is conducted between two places, or that a user who is participating in a conversation by using any transmission terminal leaves the conversation while the conversation is conducted among multiple places. In this case, if the communication charge for a period from start to end of the conversation is uniformly charged to a user who has not participated in the conversation for a certain period of time, the user is unfairly charged.